The present invention relates, in general, to the field of circulating fluidized bed (CFB) boilers and, in particular, to improved impact type particle separator constructions comprising fluid-cooled tubes.
CFB boiler systems are known and used in the production of steam for industrial processes and/or electric power generation. See, for example, U.S. Pat. Nos. 5,799,593, 4,992,085, and 4,891,052 to Belin et al.; U.S. Pat. No. 5,809,940 to James et al.; U.S. Pat. Nos. 5,378,253 and 5,435,820 to Daum et al.; and U.S. Pat. No. 5,343,830 to Alexander et al. In CFB reactors, reacting and non-reacting solids are entrained within the reactor enclosure by the upward gas flow which carries solids to the exit at the upper portion of the reactor where the solids are separated by impact type particle separators. The impact type particle separators are placed in staggered arrays to present a path which may be navigated by the gas stream, but not the entrained particles. The collected solids are returned to the bottom of the reactor. One CFB boiler arrangement uses a plurality of impact type particle separators (or concave impingement members or U-beams) at the furnace exit to separate particles from the flue gas. While these separators can have a variety of configurations, they are commonly referred to as U-beams because they most often have a U-shaped configuration in cross-section.
When applied to a CFB boiler, a plurality of such impact type particle separators are supported within the furnace enclosure and extend vertically in at least two rows across the furnace exit opening, with collected particles falling unobstructed and unchanneled underneath the collecting members along the rear enclosure wall. The gap between each adjacent pair of U-beams in one row is aligned with a U-beam in a preceding or following row of U-beams to present a tortuous path for the flue gas/solids to navigate. The U-beams in each row collect and remove particles from the flow of flue gas/solids, while the flue gas stream continues to flow around and through the U-beam array.
These types of collection elements are generally relatively long in comparison to their width and depth. The shape of the collection elements is usually dictated by two considerations: namely, the collection efficiency of the U-beams themselves and the ability of the U-beams to be self-supporting. When these elements are used, they are generally placed at the furnace exit and not cooled. Their placement at the furnace outlet is to protect the downstream heating surfaces from erosion by solid particles. Thus, the U-beams are exposed to the high temperatures of the flowing stream of flue gas/solids, and the materials used for the U-beams must be sufficiently temperature resistant to provide adequate support and resistance to damage.
Long, self-supporting stainless steel plate channels have been successfully used in CFB boilers for the primary solids collector, but the xe2x80x9ccreepxe2x80x9d strength of the commercially available and suitable alloys limits the length of the collection elements. By breaking up the long collection channel into short segments, the required strength of each short segment is much less than for the long channel due to the series of intermittent supports and the small amount of weight of any individual segment or element.
Methods of making collection elements which are cooled or supported off a cooled structure have usually included collection plates welded to water cooled support tubes. See U.S. Pat. Nos. 5,378,253 and 5,435,820 to Daum et al. However, welding to the cooling tubes increases the opportunity for tube leaks to occur at the welds.
In addition, under this known design structure, the collection element is cooled asymmetrically due to the proximity of the cooled tube or tubes to only some portion of the shaped collection channel segment or element. Thus, the plate forming the collection elements will tend to distort due to the differential expansion of the cooler areas in comparison to the hotter portions of the collection elements.
In addition, it is necessary to protect the tubes themselves from erosion caused by the impacting solids entrained within the solid/gas flow. This protection requires the use of tube shields made of stainless steel or ceramic which must be used along the entire height of the collector, which adds further cost.
The present invention comprises various arrangements and configurations of impact type particle separators, commonly provided in a U-shape, but which can also be formed into W-, E-, V- or other shapes, which are supported by fluid-cooled tubes. Such impact type particle separators find particular use in circulating fluidized bed (CFB) boilers or reactors. The present invention separates the support function from the collection shape required by functional performance considerations, thereby reducing the strength requirements of the material used to form the collection shape. By this approach, the strength of the material from which the fluidcooled support is made is much higher due to the lower operating temperature of the material comprising the fluid-cooled support, thereby permitting the use of lower cost materials for the fluid-cooled support. In addition, by using relatively small segments to make up the functional shape of each overall impact type particle separator, the strength requirements for each segment is minimal since each collection element segment needs to support only itself.
The fluid-cooled supports generally comprise tubes cooled by a fluid such as water, steam, or other suitable cooling mediums and which are positioned in the flue gas and solids particles stream. Each collection element may be supported by a single fluid-cooled tube, or as illustrated in some embodiments, two or more fluid-cooled tubes may be used, attached to maintain their relative position with respect to each other. The segments forming the collection elements may be attached directly to the one or more fluid-cooled tubes, or they may be attached to attachments to the one or more tubes, such as by using bolts or interlocking attachments such as lugs and hooks.
If desired, the collection element segments can be attached to the fluid-cooled support in such a way as to enhance cooling of the segment if that is advantageous, such as by embedding the segments in a heat conducting cement or grout. Alternatively, the segment can be spaced off or away from the fluid-cooled support by a small gap to maintain the operating temperature of the segment close to the temperature of the surrounding flue gas and solids particles, if that is desirable. This provides for controlling the temperature of the collection element segments to promote greater resistance to corrosion and/or erosion. Sometimes U-bolts, threaded studs, welded lugs on the fluid-cooled support with hooks on the segment are used to attach the collection element segments to the fluid-cooled support. Materials for the cooled support may include carbon steel or more expensive materials such as chromium-molybdenum alloys as required for the operating service temperatures. The collection element segments comprising the impact type particle separators may be made of carbon steel, alloy steel, stainless steel, ceramics, composites, or other materials as required for the intended service conditions.
Accordingly, one aspect of the present invention is drawn to an apparatus for separating solids from a flow of flue gas in a circulating fluidized bed (CFB) boiler. In all embodiments, the apparatus comprises a plurality of vertical, impact type particle separators located within the CFB, the impact type particle separators being adjacently positioned and horizontally spaced from one another in a plurality of staggered rows. Also, each impact type particle separator includes at least one vertical fluid-cooled support tube for conveying a cooling medium therethrough and a plurality of hung elements which are supported from the at least one support tube, the plurality of hung elements cooperating with one another at adjacent ends thereof to form a collecting channel which opens toward the flow of flue gas along the length of the support tube.
The difference between the various embodiments primarily involve the constructions of the impact type particle separator elements making up the array in the CFB.
In a first embodiment, each support tube has fins and the hung elements are U-shaped having side walls and a back wall and are supported by hooks attached thereto which engage the fins from a rear side of the support tube. Each support tube is located within the U-shaped portion of the hung elements, and a C-channel having interlocking portions which engage the fins from a front side of the support tube is provided, the C-channel covering the support tube to prevent erosion thereof by solids collected by the impact type particle separator when the CFB boiler is in operation.
Alternatively, or in addition to the aforementioned protective element construction, each of the support tubes may be provided with at least one of: a plurality of pin studs welded to the support tube and covered with a coating of refractory; ceramic tiles; metal or ceramic spray coatings; metal or ceramic castings; weld overlay; and shields.
In another embodiment, each of the support tubes has fins and the hung elements are U-shaped and supported by hooks which engage the fins from a front side of the support tube. Again, the plurality of hung elements cooperate with one another at adjacent ends thereof to form the collecting channel which opens toward the flow of flue gas along the length of the support tube. Here, the collecting channel has side walls and a back wall, the back wall having a curved portion adapted to correspond to an outside diameter of the support tube, the support tube being located outside of the U-shaped portion of the hung elements.
In another embodiment, each hung element of the apparatus has a first V-shaped portion and a second V-shaped portion connected thereto which together surround the support tube and cooperate with one another at adjacent ends of the hung elements to provide the collecting channel which opens toward the flow of flue gas along the length of the support tube.
Alternatively, each hung element has a W-shaped portion and a V-shaped portion connected thereto which together surround the support tube and cooperate with one another at adjacent ends of the hung elements to provide the collecting channel which opens toward the flow of flue gas along the length of the support tube.
In both of the embodiments disclosed immediately above, there may be provided leading and trailing plate portions connected to the first and second portions and which serve to confine the flow of flue gas and solids to a particular path to enhance collection efficiency as the flue gas and solids are conveyed through the plurality of vertical, impact type particle separators located within the CFB.
In yet another embodiment, each impact type particle separator includes a pair of vertical fluid-cooled support tubes for conveying a cooling medium therethrough. The pair of support tubes are connected to one another by a membrane or plate, the plurality of hung elements being supported from the membrane or plate. Each hung element has a pair of curved portions each adapted to receive one of the pair of support tubes.
Alternatively, each impact type particle separator includes a single vertical fluid-cooled support tube for conveying a cooling medium therethrough, the single support tube having fins. The plurality of hung elements are supported by the single support tube, each hung element having a curved portion adapted to receive the single support tube and a pair of feet which rest upon the fins to support and align the hung element with respect to the flow of flue gas.
Finally, another embodiment involves a construction wherein each impact type particle separator includes a single vertical fluid-cooled support tube for conveying a cooling medium therethrough, the support tube having fins. Here, the plurality of hung elements are H-shaped and supported by and surrounding the single support tube, each H-shaped hung element having a portion adapted to receive and engage the single support tube and fins so as to support and align the hung elements with respect to the flow of flue gas.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific benefits attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.